1. Field of Invention
The present invention relates generally to an inkjet head to be used for an inkjet type printer or the like, more specifically to an inkjet head having piezoelectric device to apply positive pressure or negative pressure to ink to control ink ejection.
2. Description of the Related Art
FIG. 1 shows the configuration of a conventional inkjet head. In such an inkjet head, an ink passage 103 and a plurality of ink chambers 105 (one of which is depicted) are formed on a plate portion 104. Ink is supplied from the ink passage 103 to the ink chambers 105, and then, a piezoelectric element 101 applies pressure to the ink, so that the ink is ejected through an ink nozzle 102.
The ink ejecting action of the inkjet head is further explained with reference to FIG. 2. FIG. 2 is a sectional view taken substantially along the line IIxe2x80x94II of FIG. 1. As shown in FIG. 2, electrodes 106 to be negatively charged and electrodes 107 to be positively charged are mounted on the piezoelectric element 101. These electrodes 106 and 107 are located at positions corresponding to the ink chambers 105, respectively. By using the electrodes 106 and 107, an electric field whose direction is perpendicular to the polarization direction of the piezoelectric element 101 is applied to the piezoelectric element 101 in order to distort the piezoelectric element 101 in a shear mode (thickness shear mode). Namely, when the electric field is applied, the piezoelectric element 101 deflects inwardly into the ink chambers 105, and pressure is applied to the ink within the ink chambers 105. In such a manner, the ink ejection can be realized. In addition, the shear mode means a mode of distortion that occurs by applying an electric field whose direction is perpendicular to the polarization direction of a piezoelectric element.
Furthermore, an ink ejecting action of another inkjet head using the shear mode is explained with reference to FIG. 3. FIG. 3 is a sectional view of the inkjet head. As shown in FIG. 3, electrodes 202 to be positively charged and electrodes 203 to be negatively charged are mounted on a piezoelectric element 201. The electrodes 202 are located at positions corresponding to ink chambers 205 formed on a plate portion 204, respectively. The electrodes 203 are located at positions corresponding to side wall portions, respectively. By using the electrodes 202 and 203, an electric field whose direction is perpendicular to the polarization direction of the piezoelectric element 201 is applied to the piezoelectric element 201 in order to distort the piezoelectric element 201 in the shear mode. Thus, it is possible to apply pressure to ink within the ink chambers 205 to eject the ink.
Moreover, an ink ejecting action of an inkjet head using a distortion mode other than the shear mode is explained with reference to FIG. 4. FIG. 4 is a sectional view of the inkjet head. As shown in FIG. 4, a diaphragm 303 is disposed on ink chambers 304 formed on a plate portion 305 as an upper wall. Laminated piezoelectric members are mounted on the surface of the diaphragm 303. Each of the laminated piezoelectric members is formed of a plurality of piezoelectric elements 301 and a plurality of electrode layers 302. The piezoelectric elements 301 and the electrode layers 302 are alternately laminated. By using the electrode layers 302, an electric field whose direction is parallel to the polarization direction of the piezoelectric elements 301 is applied to the piezoelectric elements 301 in order to distort the piezoelectric elements 301 in an expansion mode (longitudinal vibration mode). Thus, it is possible to apply pressure to ink within the ink chambers 304 to eject the ink. In addition, the expansion mode means a mode of distortion that occurs by applying an electric field whose direction is parallel to the polarization direction of a piezoelectric element.
However, in the inkjet head using the shear mode shown in FIG. 2 or FIG. 3, distortion of the piezoelectric element 101 or 201 is relatively small. Therefore, it is required to apply a high voltage to the piezoelectric element 101 or 201 in order to obtain sufficient distortion to realize optimum ink ejection.
On the other hand, in the inkjet head using the expansion mode shown in FIG. 4, distortion of the each laminated piezoelectric member is relatively large. Therefore, sufficient distortion can be obtained by a low voltage. However, the diaphragm 303 is made of a soft elastic material so as not to restrict distortion of each piezoelectric element 301. Therefore, pressure which has been applied to ink within the ink chambers 304 is reduced due to the soft elasticity of the diaphragm 303.
Furthermore, in the inkjet head using the expansion mode shown in FIG. 4, the plate portion 305, the diaphragm 303, the piezoelectric elements 301, and so on are separated as independent parts, respectively. When assembling the inkjet head, these parts are accurately bonded to each other at the predetermined positions by using adhesive. Therefore, if the size of an inkjet head is reduced, the manufacture of the inkjet head is difficult.
It is therefore a first object of the present invention to provide a piezoelectric device which can be distorted largely and dynamically by low electric energy to thereby control ink ejection efficiently.
It is a second object of the present invention to provide a piezoelectric device which can be simplified its construction and its manufacturing process, providing large and dynamic distortion by low electric energy.
It is a third object of the present invention to provide an inkjet head which can be simplified its construction and its manufacturing process, improving ink ejection performance.
According to the present invention, the above mentioned objects can be achieved by a piezoelectric device for applying pressure to ink within a plurality of ink chambers formed in an inkjet head to control ejection of the ink, the piezoelectric device being mounted on a plate body of the inkjet head on which the plurality of ink chambers and a plurality of peripheral portions are alternately arranged, the piezoelectric device having: a base piezoelectric layer whose underside is fixed onto the plate body, and covering over the ink chambers and the peripheral portions, the base piezoelectric layer being polarized in a direction of its thickness; an electric field applying device for applying an electric field to the base piezoelectric layer, a direction of the electric field intersecting a polarization direction of the base piezoelectric layer; and a plurality of piezoelectric members arranged on an upside of the base piezoelectric layer, and located at positions corresponding to the ink chambers respectively. Each of the piezoelectric members has a plurality of piezoelectric layers and a plurality of electrode layers. The piezoelectric layers and the electrode layers are alternately laminated. Each of the piezoelectric layers is polarized in a direction of its thickness such that respective polarization directions of the piezoelectric layers are reversed for each of the piezoelectric layers.
In this piezoelectric device, when voltages having certain polarities are supplied to the electric field applying device, the electric field applying device generates an electric field whose direction intersects the polarization direction of the base piezoelectric layer, and applies the electric field to the base piezoelectric layer. Therefore, the base piezoelectric layer is distorted in a shear mode. As a result, the base piezoelectric layer protrudes to the inside of the ink chambers.
Furthermore, when voltages having a certain polarities are supplied to the respective electrode layers of each piezoelectric member, the electric field whose direction is parallel to the polarization direction of each of the piezoelectric layers of the piezoelectric member is generated, and applied to each of the piezoelectric layers. Therefore, each of the piezoelectric layers is distorted in an expansion mode, and the piezoelectric member as a whole expands toward the base piezoelectric layer. As a result, the piezoelectric member pushes the base piezoelectric layer, and base piezoelectric layer protrudes to the inside of the ink chambers.
Thus, the base piezoelectric layer is distorted largely and dynamically by the cooperation of the shear mode distortion and the expansion mode distortion, and therefore, pressure is applied to ink within each ink chamber to thereby eject the ink.
Consequently, it is possible to obtain large and dynamic distortion of the base piezoelectric layer efficiently. Especially, the piezoelectric member expands by applying a low voltage, and pushes the base piezoelectric layer toward the inside of each ink chamber. At this time, the base piezoelectric layer itself is distorted in the shear mode. Thus, it is possible to obtain large and dynamic distortion of the base piezoelectric layer by a low voltage, and it is possible to improve the ink ejecting performance of the inkjet head, reducing electric power consumption.
Furthermore, the base piezoelectric layer covers over the respective ink chambers. Namely, the base piezoelectric layer serves as an upper wall of each ink chamber. Since the base piezoelectric layer has relatively high stiffness, it is possible to prevent the pressure that has been applied to the ink within the ink chamber from reducing.
Moreover, the electric field applying device may have a plurality of first electrodes and a plurality of second electrodes mounted on the upside or underside of the base piezoelectric layer. The first electrodes may be located at positions corresponding to the ink chambers respectively, and the second electrodes may be located at positions corresponding to the peripheral portions respectively. Thus, the electric field whose direction intersects the polarization direction of the base piezoelectric layer can be applied to the base piezoelectric layer.
According to the present invention, the above mentioned objects can be also achieved by a piezoelectric device for applying pressure to ink within a plurality of ink chambers formed in an inkjet head to control ejection of the ink, the piezoelectric device being mounted on a plate body of the inkjet head on which the plurality of ink chambers and a plurality of peripheral portions are alternately arranged, the piezoelectric device having: an elastic layer whose underside is fixed onto the plate body, and covering over the ink chambers and the peripheral portions, the elastic layer being made of an elastic material; a base piezoelectric layer laminated on an upside of the elastic layer, the base piezoelectric layer being polarized in a direction of its thickness; a first electric field applying device for applying a first electric field to the base piezoelectric layer, a direction of the first electric field being parallel to a polarization direction of the base piezoelectric layer; and a plurality of piezoelectric members arranged on an upside of the base piezoelectric layer, and located at positions corresponding to the ink chambers respectively. Each of the piezoelectric members has a plurality of piezoelectric layers and a plurality of electrode layers. The piezoelectric layers and the electrode layers are alternately laminated. Each of the piezoelectric layers is polarized in a direction of its thickness such that respective polarization directions of the piezoelectric layers are reversed for each of the piezoelectric layers.
In this piezoelectric device, when voltages having certain polarities are supplied to the first electric field applying device, the first electric field applying device generates a first electric field whose direction is parallel to the polarization direction of the base piezoelectric layer, and applies the first electric field to the base piezoelectric layer. At this time, since the base piezoelectric layer is laminated on the elastic layer, the underside of the base piezoelectric layer is fixed onto the upside of the elastic layer. Therefore, the shrinkage of the underside of the base piezoelectric layer is restricted. Accordingly, the piezoelectric layer is distorted in a unimorph mode.
Furthermore, when voltages having a certain polarities are supplied to the respective electrode layers of each piezoelectric member, the first electric field whose direction is parallel to the polarization direction of each of the piezoelectric layers of the piezoelectric member is generated, and applied to each of the piezoelectric layers. Therefore, each of the piezoelectric layers is distorted in the expansion mode, and the piezoelectric member as a whole expands toward the base piezoelectric layer. As a result, the piezoelectric member pushes the base piezoelectric layer, and the elastic layer protrudes to the inside of the ink chambers by the distortion of the base piezoelectric layer.
Thus, the base piezoelectric layer is distorted largely and dynamically by the cooperation of the unimorph mode distortion and the expansion mode distortion, and therefore, pressure is applied to ink within each ink chamber to thereby eject the ink.
Consequently, it is possible to obtain large and dynamic distortion of the base piezoelectric layer efficiently. Especially, the piezoelectric member expands by applying a low voltage, and pushes the base piezoelectric layer toward the inside of each ink chamber. At this time, the base piezoelectric layer itself is distorted in the unimorph mode. Thus, it is possible to obtain large and dynamic distortion of the base piezoelectric layer by a low voltage, and it is possible to improve the ink ejecting performance of the inkjet head, reducing electric power consumption.
Furthermore, the first electric field applying device may have a plurality of first electrodes mounted between the elastic layer and the base piezoelectric layer. The first electric field can be applied to the base piezoelectric layer by using each of the first electrodes and one of the electrode layers included in each piezoelectric member. Namely, the electrode layer, which is included in the piezoelectric member and located at the closest position to the base piezoelectric layer, works for applying the first electric field to the base piezoelectric layer, together with the first electrode. This electrode layer and the first electrode are opposite to each other across the base piezoelectric layer. Therefore, the first electric field whose direction is parallel to the polarization direction of the base piezoelectric layer can be applied to the base piezoelectric layer.
Moreover, the piezoelectric device may have a second electric field applying device for applying a second electric field, whose direction intersects the polarization direction of the base piezoelectric layer, to the base piezoelectric layer. Therefore, it is possible to distort the base piezoelectric layer in the shear mode. Thus, the base piezoelectric layer can be distorted largely and dynamically by the cooperation of the unimorph mode distortion, the expansion mode distortion, and the shear mode distortion. Consequently, it is possible to obtain large and dynamic distortion of the base piezoelectric layer efficiently.
Moreover, the second electric field applying device may have a plurality of first electrodes and a plurality of second electrodes mounted between the elastic layer and the base piezoelectric layer. The first electrodes may be located at positions corresponding to the ink chambers respectively, and the second electrodes may be located at positions corresponding to the peripheral portions respectively. Thus, the second electric field whose direction intersects the polarization direction of the base piezoelectric layer can be applied to the base piezoelectric layer.
According to the present invention, the above mentioned objects can be achieved by a piezoelectric device for applying pressure to ink within a plurality of ink chambers formed in an inkjet head to control ejection of the ink, the piezoelectric device being mounted on a plate body of the inkjet head on which the plurality of ink chambers and a plurality of peripheral portions are alternately arranged, the piezoelectric device having: a first base piezoelectric layer whose underside is fixed onto the plate body, and covering over the ink chambers and the peripheral portions, the first base piezoelectric layer being polarized in a direction of its thickness; a second base piezoelectric layer laminated on an upside of the first base piezoelectric layer, the second base piezoelectric layer being polarized in a direction of its thickness; a first electric field applying device for applying a first electric field to each of the first base piezoelectric layer and the second base piezoelectric layer, a direction of the first electric field being parallel to a polarization direction of each of the first base piezoelectric layer and the second base piezoelectric layer; and a plurality of piezoelectric members arranged on an upside of the second base piezoelectric layer, and located at positions corresponding to the ink chambers respectively. Each of the piezoelectric members has a plurality of piezoelectric layers and a plurality of electrode layers. The piezoelectric layers and the electrode layers are alternately laminated, each of the piezoelectric layers is polarized in a direction of its thickness such that respective polarization directions of the piezoelectric layers are reversed for each of the piezoelectric layers.
In this piezoelectric device, when voltages having certain polarities are supplied to the first electric field applying device, the first electric field applying device generates a first electric field whose direction is parallel to the polarization direction of each of the first base piezoelectric layer and the second base piezoelectric layer, and applies the first electric field to each of the first base piezoelectric layer and the second base piezoelectric layer. At this time, since the second base piezoelectric layer is laminated on the first base piezoelectric layer, the underside of the second base piezoelectric layer is fixed onto the upside of the first base piezoelectric layer. Therefore, both the first base piezoelectric layer and the second base piezoelectric layer are distorted in a bimorph mode.
Furthermore, when voltages having a certain polarities are supplied to the respective electrode layers of each piezoelectric member, the electric field whose direction is parallel to the polarization direction of each of the piezoelectric layers of the piezoelectric member is generated, and applied to each of the piezoelectric layers. Therefore, each of the piezoelectric layers is distorted in the expansion mode, and the piezoelectric member as a whole expands toward the first base piezoelectric layer and the second base piezoelectric layer. As a result, the piezoelectric member pushes the first base piezoelectric layer and the second base piezoelectric layer, and the first base piezoelectric layer protrudes to the inside of the ink chambers.
Thus, the first base piezoelectric layer is distorted largely and dynamically by the cooperation of the bimorph mode distortion and the expansion mode distortion, and therefore, pressure is applied to ink within each ink chamber to thereby eject the ink.
Consequently, it is possible to obtain large and dynamic distortion of the first base piezoelectric layer efficiently. Especially, the piezoelectric member expands by applying a low voltage, and pushes the first base piezoelectric layer and the second base piezoelectric layer toward the inside of each ink chamber. At this time, the first base piezoelectric layer and the second base piezoelectric layer are distorted in the bimorph mode. Thus, it is possible to obtain large and dynamic distortion of the first base piezoelectric layer by a low voltage, and it is possible to improve the ink ejecting performance of the inkjet head, reducing electric power consumption.
Furthermore, the first base piezoelectric layer covers over the respective ink chambers. Namely, the first base piezoelectric layer serves as an upper wall of each ink chamber. Since the first base piezoelectric layer has relatively high stiffness, it is possible to prevent the pressure that has been applied to the ink within the ink chamber from reducing.
Moreover, the first electric field applying device may have: a plurality of first electrodes mounted between the first base piezoelectric layer and the second base piezoelectric layer, and located at positions corresponding to the ink chambers respectively; and a second electrode mounted on the underside of the first base piezoelectric layer, and spreads over the underside of the first base piezoelectric layer.
In this first electric field applying device, the first electric field can be applied to the second base piezoelectric layer by using each of the first electrodes and one of the electrode layers included in each piezoelectric member. Namely, the electrode layer, which is included in the piezoelectric member and located at the closest position to the second base piezoelectric layer, works for applying the first electric field to the second base piezoelectric layer, together with the first electrode. This electrode layer and the first electrode are opposite to each other across the second base piezoelectric layer. Therefore, the first electric field whose direction is parallel to the polarization direction of the second base piezoelectric layer can be applied to the second base piezoelectric layer. Furthermore, the first electric field can be also applied to the first base piezoelectric layer by using each of the first electrodes and the second electrode. The first electrode is located at the position corresponding to the ink chamber. The second electrode spreads over the ink chamber. Namely, the first electrode and the second electrode are opposite to each other across the first base piezoelectric layer. Therefore, the first electric field whose direction is parallel to the polarization direction of the first base piezoelectric layer can be applied to the first base piezoelectric layer.
Alternatively, the first electric field applying device may have: a first electrode mounted between the first base piezoelectric layer and the second base piezoelectric layer, and spreads between the first base piezoelectric layer and the second base piezoelectric layer; and a plurality of second electrodes mounted on the underside of the first base piezoelectric layer, and located at positions corresponding to the ink chambers respectively. Also, in such a construction, the first electric field whose direction is parallel to the polarization direction of each of the first base piezoelectric layer and the second base piezoelectric layer can be applied to each of the first base piezoelectric layer and the second base piezoelectric layer.
Moreover, the piezoelectric device may have: a second electric field applying device for applying a second electric field, whose direction intersects the polarization direction of each of the first base piezoelectric layer and the second base piezoelectric layer, to each of the first base piezoelectric layer and the second base piezoelectric layer. Therefore, it is possible to distort each of the first base piezoelectric layer and the second base piezoelectric layer in the shear mode. Thus, the first base piezoelectric layer can be distorted largely and dynamically by the cooperation of the bimorph mode distortion, the expansion mode distortion, and the shear mode distortion. Consequently, it is possible to obtain large and dynamic distortion of the first base piezoelectric layer efficiently.
Moreover, the second electric field applying device may have a plurality of first electrodes and a plurality of second electrodes mounted between the first base piezoelectric layer and the second base piezoelectric layer. The first electrodes may be located at positions corresponding to the ink chambers respectively. The second electrodes may be located at positions corresponding to the peripheral portions respectively. Therefore, it is possible to apply the second electric field, whose direction intersects the polarization direction of each of first base piezoelectric layer and the second base piezoelectric layer, to each of first base piezoelectric layer and the second base piezoelectric layer.
According to the present invention, the above mentioned objects can be achieved by a piezoelectric device for applying pressure to ink within a plurality of ink chambers formed in an inkjet head to control ejection of the ink, the piezoelectric device being mounted on a plate body of the inkjet head on which the plurality of ink chambers and a plurality of peripheral portions are alternately arranged, the piezoelectric device having: a first base piezoelectric layer whose underside is fixed onto the plate body, and covering over the ink chambers and the peripheral portions, the first base piezoelectric layer being polarized in a direction of its thickness; a second base piezoelectric layer laminated on an upside of the first base piezoelectric layer, the second base piezoelectric layer being polarized in a direction of its thickness; a first electric field applying device for applying a first electric field to each of the first base piezoelectric layer and the second base piezoelectric layer, a direction of the first electric field intersecting a polarization direction of each of the first base piezoelectric layer and the second base piezoelectric layer; a second electric field applying device for applying a second electric field to the second base piezoelectric layer, a direction of the second electric field being parallel to a polarization direction of the second base piezoelectric layer; and a plurality of piezoelectric members arranged on an upside of the second base piezoelectric layer, and located at positions corresponding to the ink chambers respectively. Each of the piezoelectric members has a plurality of piezoelectric layers and a plurality of electrode layers. The piezoelectric layers and the electrode layers are alternately laminated. Each of the piezoelectric layers is polarized in a direction of its thickness such that respective polarization directions of the piezoelectric layers are reversed for each of the piezoelectric layers.
In this piezoelectric device, when voltages having certain polarities are supplied to the first electric field applying device, the first electric field applying device generates a first electric field whose direction intersects the polarization direction of each of the first base piezoelectric layer and the second base piezoelectric layer, and applies the first electric field to each of the first base piezoelectric layer and the second base piezoelectric layer. Therefore, each of the first base piezoelectric layer and the second base piezoelectric layer is distorted in the shear mode, respectively.
Furthermore, when voltages having certain polarities are supplied to the second electric field applying device, the second electric field applying device generates a second electric field whose direction is parallel to the polarization direction of the second base piezoelectric layer, and applies the second electric field to the second base piezoelectric layer. At this time, since the second base piezoelectric layer is laminated on the first base piezoelectric layer, the underside of the second base piezoelectric layer is fixed onto the upside of the first base piezoelectric layer. Therefore, the second base piezoelectric layer is distorted in the unimorph mode, together with the first base piezoelectric layer. In addition, an electric field whose direction is parallel to the polarization direction of the first base piezoelectric layer is not applied to the first base piezoelectric layer. Only the electric field whose direction intersects the polarization direction is applied to the first base piezoelectric layer.
Furthermore, when voltages having a certain polarities are supplied to the respective electrode layers of each piezoelectric member, the electric field whose direction is parallel to the polarization direction of each of the piezoelectric layers of the piezoelectric member is generated, and applied to each of the piezoelectric layers. Therefore, each of the piezoelectric layers is distorted in the expansion mode, and the piezoelectric member as a whole expands toward the first base piezoelectric layer and the second base piezoelectric layer. As a result, the piezoelectric member pushes the first base piezoelectric layer and the second base piezoelectric layer, and the first base piezoelectric layer protrudes to the inside of the ink chambers.
Thus, the first base piezoelectric layer is distorted largely and dynamically by the cooperation of the shear mode distortion, the unimorph mode distortion and the expansion mode distortion, and therefore, pressure is applied to ink within each ink chamber to thereby eject the ink.
Consequently, it is possible to obtain large and dynamic distortion of the first base piezoelectric layer efficiently. Especially, the piezoelectric member expands by applying a low voltage, and pushes the first base piezoelectric layer and the second base piezoelectric layer toward the inside of each ink chamber. At this time, the second base piezoelectric layer is distorted in the unimorph mode, together with the first base piezoelectric layer. Thus, it is possible to obtain large and dynamic distortion of the first base piezoelectric layer by a low voltage, and it is possible to improve the ink ejecting performance of the inkjet head, reducing electric power consumption.
Furthermore, the first base piezoelectric layer covers over the respective ink chambers. Namely, the first base piezoelectric layer serves as an upper wall of each ink chamber. Since the first base piezoelectric layer has relatively high stiffness, it is possible to prevent the pressure that has been applied to the ink within the ink chamber from reducing.
The inkjet head having the aforementioned piezoelectric device can be manufactured by the following processes. First, a plurality of electrodes are formed at predetermined positions on the upside of a base piezoelectric layer. Next, a plurality of piezoelectric layers are laminated on the upside of the base piezoelectric elements. At this time, an electrode has been formed on the upside of each of the piezoelectric layers. Next, the base piezoelectric layer and the laminated piezoelectric layers are sintered. Next, the base piezoelectric layer and the laminated piezoelectric layers are polarized, respectively. Next, a part of the laminated piezoelectric layers located at the position corresponding to each of peripheral portions is removed. Thus, the piezoelectric device is completed. Next, the underside of the base piezoelectric layer of the piezoelectric device is attached onto a plate body on which the ink chambers and peripheral portions have been alternately arranged. Next, a holding member is attached onto the top portion of the laminated piezoelectric layers of the piezoelectric device. In this manufacturing method, the inkjet head can be manufactured easily.
The inkjet head having the aforementioned piezoelectric device can be also manufactured by the following another processes. First, a plurality of electrodes are formed at predetermined positions on the upside of a base piezoelectric layer. Next, a plurality of piezoelectric members are formed at positions corresponding to the ink chambers on the upside of the base piezoelectric layer by laminating a plurality of piezoelectric layers on the upside of the base piezoelectric layer. At this time, each of the piezoelectric layers has a shape corresponding to an opening shape of each ink chamber, and an electrode has been formed on the upside of each of the piezoelectric layers. Next, the base piezoelectric layer and the laminated piezoelectric layers of the piezoelectric members are sintered. Next, the base piezoelectric layer and the laminated piezoelectric layers of the piezoelectric members are polarized, respectively. Thus, the piezoelectric device is completed. Next, the underside of the base piezoelectric layer of the piezoelectric device is attached onto a plate body on which the ink chambers and peripheral portions have been alternately arranged. Next, a holding member is attached onto the top portion of each of the piezoelectric members of the piezoelectric device. In this manufacturing method, the inkjet head can be manufactured easily.
The nature, utility, and further feature of this invention will be more clearly apparent from the following detailed description with respect to preferred embodiments of the invention when read in conjunction with the accompanying drawings briefly described below.